Reduced Alternator Charging Over 12 Autocross Runs

Raced the Camaro at an event this weekend and noticed that by the end of the weekend, my voltage was getting low.   I had tested the alternator before the event and it was charging.  At the start of the event I could rev the motor and see the volts go up with RPM, well into the high 13s.  By the end of the weekend, that same revving got me maybe just over 12 volts.

I pulled the engine logs and confirmed what I was seeing at the time was real.  Peak 13.7v  at the start of the weekend and the same RPMs at the end of the second day got me 12.0v.  The voltage does increase with RPM, but just not as much as the weekend went on.

I'm going to pull the alternator to have it tested, but it's basically a brand new unit.  Could a failing battery (Optima Yellow) cause this sort of thing?  I keep it on a charger when the car isn't out at events (no street driving) but it has been abused and run low in the past, and is dated 10/19.

Anything else I should check out?

First place to check would be the Ground from the Battery to the frame.

FWIW

The alternator could be crapping out when hot.  Especially if it is a "high capacity" alternator that shoves 10 pounds of stuff into a 5 pound frame.

Check it again now that it's cooled off. I have a lot of experience with adapting alternators into cars not meant for them. Heat has a big (negative) effect on their output, and it may be a case of normal operation. I'm assuming that this is the first time that you've notice, but it may well have been happening all along... maybe... or it could be a case of slow failure. Is the regulator built into the alternator or in a separate box?

RacingComputers said:

First place to check would be the Ground from the Battery to the frame.

 

FWIW

Things get a little interesting there.

The ECU (Holley Sniper) is connected directly to the battery (positive, negative, and a relay triggered positive for ignition).  That ignition source wire is also how the ECU measures and logs voltage.  I have another volt meter tied into the other side of the system (see CARTEK below) and they are usually close, but not always in agreement.

The rest of the car uses a CARTEK BATTERY ISOLATOR GT - https://www.cartekmotorsport.com/battery-isolators/

As far as I can tell and measure, the grounding is good.

Pete. (l33t FS) said:

The alternator could be crapping out when hot.  Especially if it is a "high capacity" alternator that shoves 10 pounds of stuff into a 5 pound frame.

Alternator is a Powermaster unit spec'd by the folks there.  Not saying that isn't possible, but disappointing if that's the case.  It wasn't a hot day and the car never really got over 200 degrees, and the hood is well vented.

kb58 said:

Check it again now that it's cooled off. I have a lot of experience with adapting alternators into cars not meant for them. Heat has a big (negative) effect on their output, and it may be a case of normal operation. I'm assuming that this is the first time that you've notice, but it may well have been happening all along... maybe... or it could be a case of slow failure. Is the regulator built into the alternator or in a separate box?

I will check it out this weekend.  I've currently pulled the battery and have it sitting off the tender to see if it's holding voltage. 

This is the first time I've noticed because, to be honest, it's the first time in three years the alternator has been working and charging the battery (wiring issue before).  The battery that is in the car now had been run as a total loss battery by accident, which probably didn't help things.

Regulator is built into the unit, so I might take it to the local alternator shop this weekend and have them just give it a once over for cheap piece of mind.

I have had alternators that worked fine cold but would start to go wiggy after 90 minutes of driving.  

Local old-timer shop tested the alternator and everything looked good.  They want me to confirm the ground and make sure I'm not getting any belt slip.